Onions, a remedy for cough?

After a long pause in writing, I am looking forward to being more active here, and sharing the result of my browsing and researching. These past years have been filled with constant research but very little time to actually summarize and write the result of those long (often night-time) sessions. Where should I start?

We all have a lot on our minds right now. The world is pushing and pulling in all different directions, and never have we felt more divided. And this is a pretty disturbing feeling. In the midst of all this division though, I think we can at least agree that we need to support our immune systems, and that we need to look for help everywhere we can, starting from what is a the center of our every day life: food, and natural ingredients.

Is anybody coughing around here?

This winter has brought respiratory symptoms to many of us. And whether we are dealing with a mild cold or a more severe disease, we all could use some help, especially coming from comforting ingredients we often have lying around. As I was recently looking for ways to relieve a (mild) cough, I found recommendations to cut an onion open and to leave it close to the bed at night. I also found advice to infuse onion pieces in water for a few hours and to drink spoons of the liquid regularly. And I wondered if there was any truth to those.

A short research revealed that as a matter of fact, onions have been used since ancient times for their therapeutic properties, and more recently studied for their effects on many physiological systems, including respiratory function. But are they truly useful?

Is there anything special about onions?

Onions (Allium cepa) have been used in food, spice and herbal preparations for at least 7,000 years and originated from Central Asia, Pakistan, or Iran. The plant has hollow leaves and flowers, but the part that is used for food and medicinal preparations is the bulb that develops underground. Even though onions possess many interesting culinary and therapeutic properties, it is important to note that they are toxic to cats and dogs and many other animals and therefore, any onion-based remedy should not be used on pets.

Traditionally, Ayurveda and Chinese medicines have used various preparations of Allium cepa, as decoction, infusion, juice, raw, or cooked bulb as treatment for different ailments including fever, headache, common cold, and chronic bronchitis. However, more recent studies have investigated in a systematic way the effects of onion extract on several diseases and physiological functions and have confirmed many interesting therapeutic properties of A. cepa.

Effects of onion extracts on respiratory function

Extracts of onions have been shown to have effects on various parts of the respiratory system.

In rats, onion extracts have a relaxing effect on smooth bronchial muscles of the lungs, which leads to widen air passages and easier breathing (bronchodilation). A. cepa extracts also reduce inflammation and tracheal responsiveness in asthmatic rats, therefore acting as a preventive against asthma attacks. Topical application of onion extracts decreases symptoms of allergic rhinitis in mice.

In humans, Quercetin, an important component of onion extracts has been shown to help asthma symptoms. And in case of mild viral flu, inhalations of a preparation of onion, garlic, or scallions have been described as improving all symptoms at the onset of disease.

Which components are responsible for the therapeutic properties of onions?

Onions have many constituents, including flavonoids, thiosulphinates and phenolic acids. The flavonoids that are contained in the onion skin, such as quercetin and kaempferol, have important roles in health, with antiviral, antimicrobial, anti-inflammatory, anticancer, and immuno-modulatory activities. Quercetin has been widely studied and the anti-inflammatory, antiviral and antimicrobial effects seem to be particularly important for lung and respiratory health. Quercetin even shows promising associations with lesser risk of lung cancer.

What type of onion preparation and quantity are useful?

Many of the studies reported in the reviews are animal studies (rats, guinea pigs, mice), therefore not directly transposable to humans, however they are a good starting point. Different types of extracts were used, either in water, or in alcohol, or other solvents such as chloroform, and solutions were administered to the animals orally, injected in the abdomen, or used as an organ bath.

Clinical studies in human populations describe the use of inhalations of preparations of onions, ingestion of raw or cooked onions, or the topical application of onion seeds in the nose (for allergic rhinitis). It is however important to note that allergies to onion constituents can occur, in particular when using cooked onions.

As far as quantity is concerned, many clinical studies use quercetin at 500 to 1000 mg per day. A heavy consumption of quercetin-containing foods such as apples and onions might provide up to 500mg per day. This dose may be boosted by concurrent ingestion of fats or pectin that increase absorption.

In conclusion

In conclusion, onions can really have beneficial effects on respiratory function and can help fight a cough, by displaying anti-inflammatory, antiviral and antimicrobial activities. However, in order to benefit from these properties, it might be necessary to ingest a higher quantity than what can be delivered just by placing an onion close to a bed or by attaching a piece of onion under the feet.

As an additional piece of hope in relation with the current situation of the world, it is interesting to note that specific components of A. cepa are currently being tested for their potential effects on COVID-19. Computational modeling predicts promising molecular interactions (binding) between specific proteins contained in onions and a critical SARS-CoV-2 enzyme (3C-like protease). Obviously, these studies are very preliminary but it is exciting to think that help in fighting COVID could hide in common foods and ingredients.

References used in this article

Effects of Allium cepa and Its Constituents on Respiratory and Allergic Disorders: A Comprehensive Review of Experimental and Clinical Evidence.

Pharmacological Properties of Allium cepa, Preclinical and Clinical Evidences; A Review

The Pharmacological Activity, Biochemical Properties, and Pharmacokinetics of the Major Natural Polyphenolic Flavonoid: Quercetin

Quercetin and Vitamin C: An Experimental, Synergistic Therapy for the Prevention and Treatment of SARS-CoV-2 Related Disease (COVID-19)

In silico screening of Allium cepa phytochemicals for their binding abilities to SARS and SARS-CoV-2 3C-like protease and COVID-19 human receptor ACE-2

Copyright (see copyright page): © “Food, Science and Health” (FoodScienceHealth.com) by Barbara Cerf-Allen, 2013 All Rights Reserved

Disclaimer: I am not advocating any of the above mentioned diets or supplements, nor am I making any claim about their usefulness for your specific condition. I am not a medical doctor and I am not giving medical advice. This blog is about sharing scientific information and my personal anecdotal experiences.

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